In general, a pneumatic tire is formed from a pair of right and left bead portions, a pair of right and left side walls, and a tire tread portion extending between both of the side walls. A carcass layer embedded with fiber cords is mounted between the pair of bead portions. An end of the carcass layer is folded around a bead core and a bead filler from a tire inner side to a tire outer side and turned up.
Generally, the bead filler is required to possess a high modulus from the viewpoint of suppressing movement of the bead portion and the end of carcass. Also, the bead filler requires low heat build-up from the viewpoint of fuel economy.
An example of a rubber composition for a bead filler is disclosed in Patent Document 1. This rubber composition for a tire bead filler contains a rubber component and a carbon black, and the rubber component contains a natural rubber and a styrene-butadiene rubber (SBR).